System and Method for Distributing Application Traffic to Servers Based on Dynamic Service Response Time

ABSTRACT

A service gateway processes a service request received from a host by: relaying the service request from the service gateway to a server over a service session between the service gateway and the server; determining a service request time for the service session; receiving by the service gateway a service response from the server; determining by the service gateway a service response time; calculating by the service gateway a service processing time for the service request from the service request time and the service response time; comparing the service processing time with an expected service processing time; and updating a server busy indicator for the server in response to the comparing. If the service processing time exceeds the expected service processing time, the server busy indicator is updated to indicate that the server is busy. Otherwise, the server busy indicator is updated to indicate that the server is not busy.

BACKGROUND OF THE INVENTION

1. Field

This invention relates generally to data communications, and more specifically, to a method and system for distributing application traffic to servers based on service process parameters.

2. Background

Web services and cloud computing are deployed in an unprecedented pace. New servers are unloaded and installed at datacenters every day. Demands of web services and corporate computing come from all directions. Consumer oriented services include smartphone apps, mobile applications such as location based services, turn-by-turn navigation services, e-book services such as Kindle™, video applications such as YouTube™ or Hulu™, music applications such as Pandora™ or iTunes™, Internet television services such as Netflix™, and many other fast growing consumer Web services. On the corporate front, cloud computing based services such as Google™ docs, Microsoft™ Office Live and Sharepoint™ software, Salesforce.com™'s on-line software services, tele-presence and web conferencing services, and many other corporate cloud computing services.

As a result more and more servers are deployed to accommodate the increasing computing needs. Traditionally these servers are managed by a service gateway such as Application Delivery Controller or Server Load Balancer (ADC/SLB) are typically network appliances in a fixed module or in a Chassis or a software module running in a commoditized server ADC/SLB manage the application traffic to servers based on incoming service requests. Common methods to distribute traffic among servers is to distribute the service requests based on the applications (HTTP, FTP, HTTPS etc.), service addresses such as URL, priorities based on network interfaces or host IP addresses. ADC/SLB may distribute the service requests to a server assuming the server is fully available to handle the service requests. Typically a fully loaded server does not handle service requests well. In fact, most if not all service requests suffer delay or no service available when a server is busy. It is often better not to further distribute service request to a busy server. Current ADC/SLB allows a network administrator to set a maximum service session capacity so that ADC/SLB does not send more than the maximum capacity service requests to the server. However, statically configured limitation on a server cannot fully utilize the server's capacity and not all service requests require the same processing from the server. It is beneficial for an ADC/SLB to determine if a server is busy based on the service response time from a server such that the ADC/SLB can reduce sending further service requests to the server.

Therefore, there is a need for a system and method for an ADC/SLB to protect a server overloading based on dynamic service response time.

BRIEF SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a method for processing a service request received from a host, comprises: (a) relaying the service request from a service gateway to a server over a service session between the service gateway and the server; (b) determining by the service gateway a service request time for the service session; (c) receiving by the service gateway a service response from the server; (d) determining by the service gateway a service response time; (e) calculating by the service gateway a service processing time for the service request from the service request time and the service response time; (f) comparing the service processing time with an expected service processing time; and (g) updating a server busy indicator for the server in response to the comparing.

In one aspect of the present invention, the updating (g) comprises: (g1) in response to determining that the service processing time exceeds the expected service processing time, updating the server busy indicator by the service gateway to indicate that the server is busy; and (g2) in response to determining that the service processing time does not exceed the expected service processing time, updating the server busy indicator by the service gateway to indicate that the server is not busy.

In one aspect of the present invention, the calculating (e) comprises: (e1) calculating by the service gateway the service processing time for the service request as a duration between the service request time and the service response time.

In one aspect of the present invention, the service response comprises an error indication, wherein the service gateway does not calculate the service processing time if the error indication indicates an error.

In one aspect of the present invention, the comparing (f) comprises: (f1) configuring the expected service processing time by the service gateway according to a service attribute of the service request or the server.

In one aspect of the present invention, the expected service processing time is associated with the service attribute and stored in a datastore, wherein the configuring (f1) comprises: (f1i) comparing by the service gateway the service request or the server with the service attribute in the datastore; and (f1ii) if the service request or the server matches the service attribute in the datastore, retrieving the expected service processing time associated with the matching service attribute.

In one aspect of the present invention, the comparing (f) further comprises: (f2) calculating an adjusted expected service processing time based on the service processing times of previous service sessions between the secure gateway and the server.

In one aspect of the present invention, the relaying (a) comprises: (a1) receiving the service request from the host by the service gateway; (a2) checking the server busy indicator for the server by the service gateway; (a3) in response to determining that the server busy indicator indicates that the server is busy, placing the service request in a service request buffer by the service gateway; and (a4) in response to determining that the server busy indicator indicates that the server is not busy, relaying the service request from the service gateway to the server over the service session between the service gateway and the server.

In one aspect of the present invention, the relaying (a4) comprises: (a4i) checking if the service request buffer is empty by the service gateway; (a4ii) in response to determining that the service request buffer is empty, relaying the service request from the service gateway to the server over the service session between the service gateway and the server; and (a4iii) in response to determining that the service request buffer is not empty, placing the service request in the service request buffer by the service gateway.

In one aspect of the present invention, the placing (a3) comprises: (a3i) determining by the service gateway if a timer at the service gateway has expired; and (a3ii) in response to determining that the timer has expired, relaying the service request from the service gateway to the server over the service session between the service gateway and the server.

In one aspect of the present invention, the service request is associated with a priority, wherein the server request buffer is configured to store service requests associated with the priority, wherein the placing (a3) comprises: (a3i) placing the service request in the service request buffer by the service gateway; and (a3ii) relaying the service request in the service request buffer from the service gateway to the server according to the associated priority.

System and computer program products corresponding to the above-summarized methods are also described and claimed herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE FIGURES

FIG. 1 illustrates a service session between a service gateway and a server.

FIG. 2 illustrates an embodiment of a method for processing a service request by a service gateway.

FIG. 3 illustrates an embodiment of a method for determining if server is busy.

FIG. 4 illustrates an embodiment of a method for processing service request based on server busy indicator.

FIG. 5 illustrates an embodiment of a method for processing service requests after service gateway updates server busy indicator.

FIG. 6 illustrates an embodiment of a method for processing service requests based on a service priority.

FIG. 7 is a flowchart illustrating an embodiment of a method for processing a service request by a service gateway.

FIG. 8 is a flowchart illustrating an embodiment of a method for processing service request based on server busy indicator.

DETAILED DESCRIPTION OF THE INVENTION

The invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, etc.

Furthermore, the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport eh program for use by or in connection with the instruction execution system, apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards, displays, point devices, etc.) can be coupled to the system either directly or through intervening I/O controllers.

Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified local function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

FIG. 1 illustrates a service session 321 between a service gateway 110 and a server 200. The service gateway 110 receives a service request 301 from a host 100. Service request 301 is delivered over a data network 153. In one embodiment, service request 301 is a Web service request such as a HTTP (Hypertext Transport Protocol) request, a secure HTTP request, a FTP (File Transfer Protocol) request, a file transfer request, a SIP (Session Initiation Protocol) session request, a request based on Web technology, a video or audio streaming request, a Web conferencing session request, or any request over the Internet or corporate network.

Host 100 is a computing device with network access capabilities. The host 100 is operationally coupled to a processor 103 and a computer readable medium 104. The computer readable medium 104 stores computer readable program code for implementing the various embodiments of the present invention as described herein. In one embodiment, host 100 is a workstation, a desktop personal computer or a laptop personal computer. In one embodiment, host 100 is a Personal Data Assistant (PDA), a smartphone, or a cellular phone. In one embodiment, host 100 is a set-top box, an Internet media viewer, an Internet media player, a smart sensor, a smart medical device, a net-top box, a networked television set, a networked DVR, a networked Blu-ray player, or a media center.

In one embodiment, data network 153 is an Internet Protocol (IP) network. In one embodiment, data network 153 is a corporate data network or a regional corporate data network. In one embodiment, data network 153 is an Internet service provider network. In one embodiment, data network 153 is a residential data network. In one embodiment, data network 153 includes a wired network such as Ethernet. In one embodiment, data network 153 includes a wireless network such as a WiFi network, or cellular network.

The service gateway 110 is operationally coupled to a processor 113 and a computer readable medium 114. The computer readable medium 114 stores computer readable program code, which when executed by the processor 113, implements the various embodiments of the present invention as described herein. In some embodiments, service gateway 110 is implemented as a server load balancer, an application delivery controller, a service delivery platform, a traffic manager, a security gateway, a component of a firewall system, a component of a virtual private network (VPN), a load balancer for video servers, or a gateway to distribute load to a plurality of servers.

Server 200 is operationally coupled to a processor 213 and a computer readable medium 214. The computer readable medium 214 stores computer readable program code, which when executed by the processor 213, implements the various embodiments of the present invention as described herein. In some embodiments, the computer readable program code implements server 200 as a Web server, a file server, a video server, a database server, an application server, a voice system, a conferencing server, a media gateway, a SIP server, a remote access server, a VPN server, or a media center.

Service gateway 110 connects to server 200 via data network 155. In one embodiment, data network 155 is the same as data network 153. In one embodiment, data network 155 is different from data network 153. In one embodiment, host 100 does not have direct access to data network 155. In one embodiment, host 100 has direct access to data network 155.

FIGS. 2 and 7 illustrate an embodiment of a method for processing a service request 301 by service gateway 110. In an embodiment, service gateway 110 receives service request 301 from host 100, and relays service request 301 to server 200 (701) by establishing service session 321 between service gateway 110 and server 200. Service gateway 110 determines a service request time 361 for service session 321 (702). In one embodiment the service request time 361 is a time stamp such as a time of the day, a system time, a time counter. In one embodiment service request time 361 is a time when service gateway 110 sends service request 301 to server 200. In one embodiment, service request time 361 is a time when service gateway 110 receives from server 200 an acknowledgement of receiving service request 301.

After server 200 processes service request 301, server 200 responds with a service response 352. In one embodiment, service response 352 includes a web page, a document, a file, a picture, a streaming of audio or video signals, or a voice call. In one embodiment, service response 352 includes an error indication 354. Error indication 354 may include a HTTP error status code, a FTP error code, SIP error message, or any other error code.

Service gateway 110 receives service response 352 and relays the service response 352 to host 100 (703). Service gateway 110 determines service response time 362 upon receipt of service response 352 (704). In an embodiment, service response time 362 is a time stamp such as a time of the day, a system time, a time counter, and is compatible with service request time 361. In one embodiment, service response time 362 is a time when service gateway 110 receives service response 352. In one embodiment, service response time 362 is a time when service gateway 110 receives first piece of information of service response 352. In one embodiment, service response time 362 is a time when service gateway 110 receives the last piece of information of service response 352. In one embodiment, service response time 362 is a time when service gateway 110 disconnects service session 321 from server 200. In one embodiment, service response time 362 is included in service response 352.

After determining service request time 361 and service response time 362, service gateway 110 calculates service processing time 360 for service request 301 from the service request time and service response time (705). Service processing time 360 typically measures the duration between service request time 361 and service response time 362. In one example, service gateway 110 subtracts service request time 361 from service response time 362 to obtain service processing time 360. In another example, service gateway 110 calculates the duration between service request time 361 and service response time 362 to determine service process time. For example, service processing time 360 is 10 milliseconds, 5 milliseconds, 247 milliseconds, 3 seconds, 15 seconds, 1 minute, 75 microseconds, or 289 units of time.

In one embodiment, service gateway 110 verifies service response 352 prior to calculating service processing time 360. In an example, service gateway 110 verifies service response 352 if the response contains an error indication 354. In one embodiment, if there is an error indicated in error indication 354, service gateway 110 does not calculate service processing time 360 for the service request 301.

In one embodiment, service gateway 110 includes a completed service session counter 326, which counts the number of completed service sessions between service gateway 110 and server 200. In one embodiment, service gateway 110 increments the completed service session counter 326 by 1 after service gateway 110 receives service response 352 or after service gateway 110 disconnects service session 321 from server 200. In one embodiment, service gateway 110 increments the completed service session counter 326 by 1 after determining service processing time 360.

FIG. 3 illustrates an embodiment of a method for determining if server 200 is busy. Service gateway 110 includes a server busy indicator 378 for server 200, indicating if server 200 is busy. In one embodiment, a value of 0 or ‘Not Busy’ for server busy indicator 378 indicates server 200 is not busy while a value of 1 or ‘Busy’ indicates server 200 is busy. Service gateway 110 updates server busy indicator 378 based on service processing time 360.

In one embodiment, service gateway 110 includes an expected service processing time 374. Referring to both FIGS. 3 and 7, service gateway 110 compares service processing time 360 with expected service processing time 374 (706). In response to determining that the service processing time exceeds expected service processing time 374, service gateway 110 updates server busy indicator 378 to ‘Busy’ (708). In one embodiment, service processing time 360 needs to be at least 50% larger than expected service processing time 374 in order to exceed expected service processing time 374. In one embodiment, service processing time 360 needs to be at least 300% larger than expected service processing time 374. In one embodiment, service processing time 360 needs to be larger than expected service processing time 374.

In one embodiment, service gateway 110 determines service processing time 360 does not exceed expected service processing time 374 (707), and in response, service gateway 110 updates server busy indicator 378 to ‘Not Busy’ (709).

In an embodiment, expected service processing time 374 is based on service request 301. In one embodiment, service request 301 comprises a service request Universal Resource Locator (URL). In one embodiment, expected service processing time 374 is configured according to a service attribute 379. The service attribute 379 is an attribute affecting the expected service processing time 374. For example, different protocols would process service requests at different rates, and thus would have different expected service processing times. In an embodiment, service attribute 379 is based on service request URL. In an embodiment, service attribute 379 is based on part of service request URL such as the domain name, a web folder name in the web site, a document type, a protocol indicated in service request URL. For example, service request URL is “http://www.abc.com/shops/shoe.html”. Service attribute 379 is based on domain name “www.abc.com”, web folder “www.abc.com/shops”, document type .html (or other document type such as .php, .asp etc.), protocol http (or other protocols such as ftp, https, sip etc.). In an embodiment, service attribute 379 is related to program code implemented on server 200. For example, server 200 is a web server using Apache web server software, Microsoft web server software, Oracle web server software or other web server software. Service attribute 379 is related to the web server software.

In one embodiment, service attribute 379 is based on domain name “www.a10networks.com” and the expected service processing time 374 is 10 milliseconds. In one embodiment, service attribute 379 is based on HTTP protocol and the expected service processing time 374 is 75 milliseconds. In one embodiment, service attribute 379 is based on FTP file download protocol and the expected service processing time 374 is 2 minutes. In one embodiment, service attribute 379 is based on HTML document type and the expected service processing time 374 is 20 milliseconds.

In one embodiment, service attribute 379 relates to program code implemented on server 200. In an embodiment, server 200 uses Apache web server software and expected processing time is 50 milliseconds. In an embodiment, server 200 uses Microsoft web server software and expected processing time is 90 milliseconds.

In one embodiment, service attribute 379 relates to a plurality of attributes mentioned in above description. Expected processing time may be determined by a summation of a plurality of expected processing times for the plurality of attributes.

In one embodiment, service gateway 110 includes a datastore 380, which stores the expected service processing time 374 and associated service attribute 379. In an embodiment, service gateway 110 compares service request 301 or server 200 against service attribute 379 in datastore 380. If there is a match, service gateway 110 retrieves expected service processing time 374 associated with the matched service attribute 379, and compares the retrieved expected service processing time 374 with the service processing time 360. In one embodiment, expected service processing time 374 is not related to any service attribute. Service gateway 110 retrieves expected service processing time 374 and compares to service processing time 360.

In one embodiment, expected service processing time 374 is configured by a user.

In one embodiment, expected service processing time 374 is automatically determined based on service processing times of previous service sessions. Upon determining service processing time 360, service gateway 110 calculates an adjusted expected service processing time 376 by using the formula:

${{adjusted}\mspace{14mu} {expected}\mspace{14mu} {service}\mspace{14mu} {processing}\mspace{14mu} {time}} = \frac{\begin{matrix} {\begin{pmatrix} {{expected}\mspace{14mu} {service}\mspace{14mu} {processing}\mspace{14mu} {time}*} \\ \left( {{{completed}\mspace{14mu} {service}\mspace{14mu} {session}\mspace{14mu} {counter}} - 1} \right) \end{pmatrix} +} \\ \left. {{service}\mspace{14mu} {processing}\mspace{14mu} {time}} \right) \end{matrix}}{{completed}\mspace{14mu} {service}\mspace{14mu} {session}\mspace{14mu} {counter}}$

In this embodiment, service gateway 110 calculates adjusted expected service processing time 376 prior to changing competed service session counter 325. In one embodiment, service gateway 110 does not adjust expected service processing time 374 if service processing time 360 exceeds expected service processing time 374, or if service response 352 includes an error indication 354. In this embodiment, service gateway 110 does not change completed service session counter 326.

In one embodiment, expected service processing time 374 is associated with service attribute 379. Completed service session counter 326 is also associated with service attribute 379 in order to implement separate counters for each service attribute. Service gateway 110 checks if service request 301 or server 200 matches service attribute 379 prior to calculating adjusted expected service processing time 376.

In one embodiment, service gateway 110 replaces expected service processing time 374 with adjusted expected service processing time 376. The adjusted expected service processing time 376 becomes the expected service processing time 374 for the next service session between the service gateway 110 and the server 200.

After the service gateway 110 updates server busy indication, the service gateway 110 receives a next service request from the host (71) and the process repeats.

FIGS. 4 and 8 illustrate an embodiment of a method for processing service request 301 based on server busy indicator 378. In one embodiment, service gateway 110 includes a service request buffer 331. In an embodiment, service gateway 110 receives service request 301 from host 110 (801). In an embodiment, service gateway 110 puts service request 301 into service request buffer 331. In another embodiment, service gateway 110 checks server busy indicator 378 (802). When the server busy indicator 378 indicates server 200 is ‘Busy’ (803), service gateway 110 places service request 301 into service request buffer 331 (804). In one embodiment, when server busy indicator 378 indicates server 200 is ‘Not Busy’ (803), service gateway 110 relays service request 301 to server 200 (701), as described above with FIGS. 2 and 7. In yet another embodiment, when server busy indicator 378 indicates server 200 is ‘Not Busy’, service gateway 110 checks if service request buffer 331 is empty (805). If service request buffer 331 is empty, service gateway 110 relays service request 301 to server 200 (701). If service request buffer 331 is not empty, the service gateway 110 places service request 301 into service request buffer 331 (806). The service gateway 110 then relays each service request in the service request buffer 331 to server 200 (701) until the service request buffer 331 is empty or until the server busy indicator 378 is changed to ‘Busy’.

FIG. 5 illustrates an embodiment of a method for processing service requests after service gateway 110 updates server busy indicator 378. Service gateway 110 processes service request 301 in service request buffer 331 according to different values of server busy indicator 378. In one embodiment, server busy indicator 378 has an updated value of ‘Not Busy’. Service gateway 110 examines service request buffer 331 and finds service request 301. Service gateway 110 replays service request 301 to server 200 (701).

In one embodiment, server busy indicator 378 has an updated value of ‘Busy’. In one embodiment, service gateway 110 does not immediately process service request buffer 331. Service gateway 110 includes a timer 119. When timer 119 expires, service gateway 110 finds the service request 301 in the service request buffer 331 and relays service request 301 in service request buffer 331 to server 200 (701). Timer 119 may be configured for duration of, for example, 1 minute, 30 seconds, 1 second, 400 milliseconds, 5 milliseconds, 300 microseconds, or any other duration such that service to service request 301 is not severely affected. In one embodiment, time duration is based on attributes of the service request 301.

FIG. 6 illustrates an embodiment of a method for processing service requests based on a service priority. In one embodiment, service request 303 is associated with a service priority 403. In a scenario, service priority 403 is based on service request 303 URL. In one scenario, service priority 403 is based on host 100, such as host 100 IP address, host 100 user identity. In one scenario, service priority 403 is associated to the network interface from which service gateway 110 receives service request 303. Service gateway 110 determines service priority 403 of service request 303.

Service request buffer 331 is configured to store service requests with service priority 401. In the embodiment where server busy indicator 378 has an updated value of ‘Busy’, service gateway 110 compares service priority 403 to service priority 401. In response to finding a match, service gateway 110 places service request 303 into service request buffer 331.

In one embodiment, service gateway 110 includes a second service request buffer 332. Service request buffer 332 is configured to store service request with service priority 402, which is higher than service priority 401.

In the embodiment where server busy indicator 378 has an updated value of ‘Not Busy’, service gateway 110 processes service requests in service request buffer 332 prior to service request buffer 331. In one embodiment, service gateway 110 sends service request 302 in service request buffer 332 to server 200 prior to sending service request 301 in service request buffer 331 to server 200.

In one embodiment, service gateway 110 processes all service requests from service request buffer 332 before processing service request buffer 331. In one embodiment, service gateway 110 includes a serving ratio 117 wherein service gateway 110 processes service request buffer 332 and service request buffer 331 according to ratio 117, where serving ratio 117 favors high priority service request buffer 332 to the lower priority service request buffer 331 in order to avoid starving the lower priority service requests in service request buffer 331.

Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. 

1. A method for processing a service request received from a host, comprising: (a) relaying the service request from a service gateway to a server over a service session between the service gateway and the server; (b) determining by the service gateway a service request time for the service session; (c) receiving by the service gateway a service response from the server; (d) determining by the service gateway a service response time; (e) calculating by the service gateway a service processing time for the service request from the service request time and the service response time; (f) comparing the service processing time with an expected service processing time; and (g) updating a server busy indicator for the server in response to the comparing.
 2. The method of claim 1, wherein the updating (g) comprises: (g1) in response to determining that the service processing time exceeds the expected service processing time, updating the server busy indicator by the service gateway to indicate that the server is busy; and (g2) in response to determining that the service processing time does not exceed the expected service processing time, updating the server busy indicator by the service gateway to indicate that the server is not busy.
 3. The method of claim 1, wherein the calculating (e) comprises: (e1) calculating by the service gateway the service processing time for the service request as a duration between the service request time and the service response time.
 4. The method of claim 1, wherein the service response comprises an error indication, wherein the service gateway does not calculate the service processing time if the error indication indicates an error.
 5. The method of claim 1, wherein the comparing (f) comprises: (f1) configuring the expected service processing time by the service gateway according to a service attribute of the service request or the server.
 6. The method of claim 5, wherein the expected service processing time is associated with the service attribute and stored in a datastore, wherein the configuring (f1) comprises: (f1i) comparing by the service gateway the service request or the server with the service attribute in the datastore; and (f1ii) if the service request or the server matches the service attribute in the datastore, retrieving the expected service processing time associated with the matching service attribute.
 7. The method of claim 5, wherein the comparing (f) further comprises: (f2) calculating an adjusted expected service processing time based on the service processing times of previous service sessions between the secure gateway and the server.
 8. The method of claim 1, wherein the relaying (a) comprises: (a1) receiving the service request from the host by the service gateway; (a2) checking the server busy indicator for the server by the service gateway; (a3) in response to determining that the server busy indicator indicates that the server is busy, placing the service request in a service request buffer by the service gateway; and (a4) in response to determining that the server busy indicator indicates that the server is not busy, relaying the service request from the service gateway to the server over the service session between the service gateway and the server.
 9. The method of claim 8, wherein the relaying (a4) comprises: (a4i) checking if the service request buffer is empty by the service gateway; (a4ii) in response to determining that the service request buffer is empty, relaying the service request from the service gateway to the server over the service session between the service gateway and the server; and (a4iii) in response to determining that the service request buffer is not empty, placing the service request in the service request buffer by the service gateway.
 10. The method of claim 8, wherein the placing (a3) comprises: (a3i) determining by the service gateway if a timer at the service gateway has expired; and (a3ii) in response to determining that the timer has expired, relaying the service request from the service gateway to the server over the service session between the service gateway and the server.
 11. The method of claim 8, wherein the service request is associated with a priority, wherein the server request buffer is configured to store service requests associated with the priority, wherein the placing (a3) comprises: (a3i) placing the service request in the service request buffer by the service gateway; and (a3ii) relaying the service request in the service request buffer from the service gateway to the server according to the associated priority.
 12. A computer program product for processing a service request received from a host, the computer program product comprising: a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code configured to: relay the service request from a service gateway to a server over a service session between the service gateway and the server; determine a service request time for the service session; receive a service response from the server; determine a service response time; calculate a service processing time for the service request from the service request time and the service response time; compare the service processing time with an expected service processing time; and update a server busy indicator for the server in response to the comparing.
 13. The product of claim 12, wherein the computer readable program code configured to update the server busy indicator for the server in response to the comparing is further configured to: in response to determining that the service processing time exceeds the expected service processing time, update the server busy indicator to indicate that the server is busy; and in response to determining that the service processing time does not exceed the expected service processing time, update the server busy indicator to indicate that the server is not busy.
 14. The product of claim 12, wherein the computer readable program code configured to calculate the service processing time for the service request from the service request time and the service response time is further configured to: calculate the service processing time for the service request as a duration between the service request time and the service response time.
 15. The product of claim 12, wherein the computer readable program code configured to compare the service processing time with the expected service processing time is further configured to: configure the expected service processing time according to a service attribute of the service request or the server.
 16. The product of claim 15, wherein expected service processing time is associated with the service attribute and stored in a datastore, wherein the computer readable program code configured to configure the expected service processing time according to a service attribute of the service request or the server is further configured to: compare the service request or the server with the service attribute in the datastore; and if the service request or the server matches the service attribute in the datastore, retrieve the expected service processing time associated with the matching service attribute.
 17. The product of claim 15, wherein the computer readable program code configured to compare the service processing time with the expected service processing time is further configured to: calculate an adjusted expected service processing time based on the service processing times of previous service sessions between the secure gateway and the server.
 18. The product of claim 12, wherein the computer readable program code configured to relay the service request from the service gateway to the server over the service session between the service gateway and the server is further configured to: receive the service request from the host; check the server busy indicator for the server; in response to determining that the server busy indicator indicates that the server is busy, place the service request in a service request buffer; and in response to determining that the server busy indicator indicates that the server is not busy, relay the service request from the service gateway to the server over the service session between the service gateway and the server.
 19. The product of claim 18, wherein the computer readable program code configured to relay the service request from the service gateway to the server over the service session between the service gateway and the server in response to determining that the server busy indicator indicates that the server is not busy is further configured to: check if the service request buffer is empty; in response to determining that the service request buffer is empty, relay the service request from the service gateway to the server over the service session between the service gateway and the server; and in response to determining that the service request buffer is not empty, place the service request in the service request buffer.
 20. The product of claim 18, wherein the computer readable program configured to place the service request in the service request buffer in response to determining that the server busy indicator indicates that the server is busy is further configured to: determine if a timer at the service gateway has expired; and in response to determining that the timer has expired, relay the service request from the service gateway to the server over the service session between the service gateway and the server.
 21. The product of claim 18, wherein the service request is associated with a priority, wherein the server request buffer is configured to store service requests associated with the priority, wherein the computer readable program configured to place the service request in the service request buffer in response to determining that the server busy indicator indicates that the server is busy is further configured to: place the service request in the service request buffer; and relaying the service request in the service request buffer from the service gateway to the server according to the associated priority.
 22. A system, comprising: a server for processing service requests; and a service gateway comprising a processor and a computer readable storage medium having computer readable program code embodied therewith, wherein when the computer readable program code is executed by the processor, causes the service gateway to: relay the service request to the server over a service session between the service gateway and the server; determine a service request time for the service session; receive a service response from the server; determine a service response time; calculate a service processing time for the service request from the service request time and the service response time; compare the service processing time with an expected service processing time; and update a server busy indicator for the server in response to the comparing.
 23. The system of claim 22, wherein the update the server busy indicator for the server in response to the comparing comprises: in response to determining that the service processing time exceeds the expected service processing time, update the server busy indicator to indicate that the server is busy; and in response to determining that the service processing time does not exceed the expected service processing time, update the server busy indicator to indicate that the server is not busy.
 24. The system of claim 22, wherein the compare the service processing time with the expected service processing time comprises: configure the expected service processing time according to a service attribute of the service request or the server.
 25. The system of claim 24, wherein expected service processing time is associated with the service attribute and stored in a datastore, wherein the configure the expected service processing time according to a service attribute of the service request or the server comprises: compare the service request or the server with the service attribute in the datastore; and if the service request or the server matches the service attribute in the datastore, retrieve the expected service processing time associated with the matching service attribute.
 26. The system of claim 24, wherein the compare the service processing time with the expected service processing time comprises: calculate an adjusted expected service processing time based on the service processing times of previous service sessions between the secure gateway and the server.
 27. The system of claim 22, wherein the relay the service request from the service gateway to the server over the service session between the service gateway and the server comprises: receive the service request from the host; check the server busy indicator for the server; in response to determining that the server busy indicator indicates that the server is busy, place the service request in a service request buffer; and in response to determining that the server busy indicator indicates that the server is not busy, relay the service request from the service gateway to the server over the service session between the service gateway and the server. 